57463-79-3Relevant articles and documents
The α-effect in hydrazinolysis of 4-chloro-2-nitrophenyl x-substituted-benzoates: Effect of substituent x on reaction mechanism and the α-effect
Kim, Min-Young,Kim, Tae-Eun,Lee, Jieun,Um, Ik-Hwan
, p. 2271 - 2276 (2014/09/29)
Second-order rate constants (kN) have been measured spectrophotometrically for the reaction of 4-chloro-2- nitrophenyl X-substituted-benzoates (6a-6h) with a series of primary amines including hydrazine in 80 mol % H2O/20 mol % DMSO at 25.0°C. The Bronsted-type plot for the reaction of 4-chloro-2-nitrophenyl benzoate (6d) is linear with βnuc = 0.74 when hydrazine is excluded from the correlation. Such a linear Bronsted-type plot is typical for reactions reported previously to proceed through a stepwise mechanism in which expulsion of the leaving group occurs in the rate-determining step (RDS). The Hammett plots for the reactions of 6a-6h with hydrazine and glycylglycine are nonlinear. In contrast, the Yukawa-Tsuno plots exhibit excellent linear correlations with ?X = 1.29-1.45 and r = 0.53-0.56, indicating that the nonlinear Hammett plots are not due to a change in RDS but are caused by resonance stabilization of the substrates possessing an electron-donating group (EDG). Hydrazine is ca. 47-93 times more reactive than similarly basic glycylglycine toward 6a-6h (e.g., the α-effect). The α-effect increases as the substituent X in the benzoyl moiety becomes a stronger electronwithdrawing group (EWG), indicating that destabilization of the ground state (GS) of hydrazine through the repulsion between the nonbonding electron pairs on the two N atoms is not solely responsible for the substituent-dependent α-effect. Stabilization of transition state (TS) through five-membered cyclic TSs, which would increase the electrophilicity of the reaction center or the nucleofugality of the leaving group, contributes to the α-effect observed in this study.
Effects of amine nature and nonleaving group substituents on rate and mechanism in aminolyses of 2,4-dinitrophenyl x-substituted benzoates
Um, Ik-Hwan,Kim, Kyung-Hee,Park, Hye-Ran,Fujio, Mizue,Tsuno, Yuho
, p. 3937 - 3942 (2007/10/03)
Second-order rate constants have been measured for the reactions of 2,4-dinitrophenyl X-substituted benzoates (1a-f) with a series of primary amines in 80 mol % H2O/20 mol % DMSO at 25.0 ± 0.1 °C. The Bronsted-type plot for the reactions of 1d with primary amines is biphasic with slopes β1 = 0.36 at the high pKa region and β2 = 0.78 at the low pKa region and the curvature center at pKa° = 9.2, indicating that the reaction proceeds through an addition intermediate with a change in the rate-determining step as the basicity of amines increases. The corresponding Bro nsted-type plot for the reactions with secondary amines is also biphasic with β1 = 0.34, β2 = 0.74, and pKa° = 9.1, indicating that the effect of amine nature on the reaction mechanism and pKa° is insignificant. However, primary amines have been found to be less reactive than isobasic secondary amines. The microscopic rate constants associated with the aminolysis have revealed that the smaller k 1 for the reactions with primary amines is fully responsible for their lower reactivity. The electron-donating substituent in the nonleaving group exhibits a negative deviation from the Hammett plots for the reactions of 1a-f with primary and secondary amines, while the corresponding Yukawa-Tsuno plots are linear. The negative deviation has been ascribed to stabilization of the ground state of the substrate through resonance interaction between the electron-donating substituent and the carbonyl functionality.
Kinetics and Mechanisms of the Aminolysis of N-Hydroxysuccinimide Esters in Aqueous Buffers
Cline, Gary W.,Hanna, Samir B.
, p. 3583 - 3586 (2007/10/02)
Rate constants for the aminolysis of the N-hydroxysuccinimide (NHS) ester of p-methoxybenzoic acid, in aqueous buffer systems (20percent dioxane), have been determined under pseudo-first-order conditions.For the amines studied (pKa = 7.60-11.1), the data fit the rate expression kobsd - kOH--> = k1free.This rate equation is in contrast to the two-term rate equation (kobsd = k1 + k22) obtained for this reaction in anhydrous dioxane (Cline, G.W.; Hanna, S.B.J.Am.Chem.Soc 1987, 109, 3087) and is suggestive of a disproportionate decrease in the catalyzed vs the uncatalyzed reaction path upon changing from a nonaqueous to an aqueous solvent system.The correlation of amine basicity with the nucleophilic rate constant, k1, yields a slope βnuc = 1.0.The magnitude of βnuc, in terms of a reaction mechanism where a tetrahedral intermediate is formed in a fast preequilibrium followed by rate-determining breakdown to products, reflects the sensitivity to changes in charge accumulation in the formation of the tetrahedral intermediate.The resultant increased rate constants, with increased basicity, are due to the effect of an increased concentration of the tetrahedral intermediate.A qualitative evaluation of the literature and current data concerning the leaving ability of N-hydroxy esters, in comparison to phenyl esters (equivalent acyl groups and nucleophiles), reveals that, with leaving groups of comparable basicity, the nucleophilic rate constants for N-hydroxy esters are about 2 orders of magnitude greater than that for phenyl esters.
